The present invention relates to a method for manufacturing a code disk for use in devices such as an optical incremenal shaft encoder or an absolute shaft encoder, and in particular to such a method wherein light-transmissive code pattern marks are generated on the disk by removal of a selected portion of an opaque layer applied to the code disk and wherein the pattern thus produced on the code disk is centered exactly relative to a shaft supporting the code disk.
Optical incremental shaft encoders and absolute shaft encoders known to those skilled in the art conventionally employ a code disk having an annular code pattern in the form of short lines or slits on the surface of the code disk. The code pattern is copied from a master by photographic means and manufactured on the code disk by a partial etching of an opaque disk which is applied on a light-transmissive disk. Other methods of manufacturing the code pattern on the code disk are known in which the pattern is generated by means of photographic recording and by conventional electro-galvanic means.
In all known methods of manufacturing a code disk, the code pattern is first generated on the disk and the disk is subsequently mounted in the device in which it is to be used. For this purpose, the code pattern produced on the disk must be subsequently centered by special measures such as, for example, by the use of a precision center bore or a light-transmissive centering circle. During assembly of the code disk on a mounted shaft, the code pattern must be exactly centered, requiring a high time outlay.